Heat-exchanging forming tool and method of making

ABSTRACT

A method of making a heat-exchanging forming tool for use in shaping articles of manufacture, said method comprising the steps of:  
     forming a non-porous metallic shell of generally uniform thickness having an outer contoured shaping surface of predetermined configuration corresponding to the desired shape to be imparted to the article by the tool on the opposite backside surface inversely contoured to that of the shaping surface;  
     supporting the shaping surface of the shell face down on an insulating support member such that the backside surface of the shell faces upwardly;  
     arranging a container over the shell;  
     introducing a plurality of discrete metallic elements into the container to provide a packed mass of such elements in contact with each other and with the backside surface of the shell and surrounding walls of the container, the elements being shaped such that when packed together the elements provide a network of interconnected open spaces throughout the packed mass of the elements; and  
     heating the elements and shell sufficiently to metallurgically bond the packed metallic elements to one another and to the shell while preserving the network of interconnected open spaces between the elements thereby obtaining a one-piece structure comprised of the non-porous metallic shell backed by an integrated porous metallic support body through which a heat exchanging fluid may be passed to conduct heat to or from the shaping surface of the shell.

CROSS REFERENCE TO RELATED CASES

[0001] This application claims the benefit of the filing of provisionalapplication Ser. No. 60/043,069, filed Apr. 8, 1997, and a continuationof U.S. Ser. No. 09/056,511, filed Apr. 7, 1998, incorporated herein byreference.

TECHNICAL FIELD

[0002] The present invention relates to the construction and method ofmaking forming tools for use in shaping articles of manufacture and moreparticularly to such tools having heat-exchanging characteristics.

BACKGROUND OF THE INVENTION

[0003] Forming tools, such as metal molds and dies, are employed in manyprocesses to impart a desired shape to an article of manufacture. Forexample, metal molds and dies are used to produce cast metal articleshaving the shape of the casting cavity of the tool. Metal dies are alsoused in other metal forming operations such as stamping, pressing,coining, drawing, extruding, forging, etc., to impart a desired shape toa metal sheet or billet. In the plastics and glass making industry,metal dies are used to shape various plastics, resins, composites, andglass to produce various shaped articles from these materials.

[0004] In many of these forming operations, such as for example thecasting of molten metal or the molding of hot plastics or glass, thereis a considerable amount of heat that must be dissipated in order tocool the article sufficiently to render the material from which thearticle is made from stable, allowing it to be released from the formingtool. It is of course desirable in many of these operations that theheat be dissipated as quickly and uniformly as possible since often therate limiting step of a given forming cycle is the time it takes toextract the heat from the article and product quality is related to theuniformity by which heat is removed from the part. As such, heattransfer efficiency and uniformity of thermal control of the formingtool used to shape the articles are key to the product quality andmanufacturing economics of the articles made from the tools. In additionto these advantages, a high efficiency forming tool reduces tooling andmanufacturing costs as fewer tools are needed to support a givenproduction schedule or schedules can be fulfilled more promptly with thetools on hand.

[0005] In accordance with one known practice, the manufacture of aforming tool, such as a metal mold, begins with a solid block of metalinto which a contoured shaping surface is machined having aconfiguration corresponding to the shape to be imparted to the articlebeing formed by the tool.

[0006] In an effort to improve the heat transfer efficiency of the solidmetal mold, it is common to bore fluid passages into the mold beneaththe shaping surface through which water, gas or other heat-transferringfluids may be passed to draw heat from the mold tool and hence thearticle. The drilling of cooling passages, however, adds to the time andcost of making the tool and further is limited in its effectivenesssince it is not always practical or possible to uniformly extend thepassages into all areas of the mold where they are required in order toachieve the desired cooling characteristics. Inadequate or nonuniformcooling of the forming tool may distort the desired shape of the articlemade by the tool.

[0007] Published International Application No. WO-96/17716, which iscommonly assigned to the assignee of the present invention, discloses aforming tool designed to dissipate heat more efficiently and uniformlythan the traditional approach described above. Disclosed is amanufacturing process for making a heat-exchanging forming tool in whicha porous heat-transferring body, such as a block of foamed metal, ismachined in much the same manner as that of the solid block describedabove to provide a contoured surface. Particles of molten metal are thenthermally sprayed onto the contoured surface of the porous block todevelop the non-porous shaping surface of the tool. The open metalnetwork of the porous body defines a tortuous flow path for coolingfluid to pass to provide rapid, uniform cooling of the shaping surfaceand thus the article being formed by the tool.

[0008] Although the porous body forming tool described in the previousparagraph is considered to be a tremendous advancement over traditionalsolid block forming tools, the method described still involves machininga contoured surface into a block of material, albeit porous, which isalso a costly and time consuming process. The described multi-layerthermal spraying process for building the non-porous shaping surface isalso costly and requires specialized equipment and skilled operators.

[0009] A principle object of the present invention is to improve onthese early developments in heat-exchanging forming tools by simplifyingthe construction and method of making high efficiency heat exchangingforming tools.

SUMMARY OF THE INVENTION

[0010] In a broad sense, the invention involves the pre-forming of anon-porous metallic shell having an outer contoured surface that servesas a shaping surface of the forming tool to be made. Once the shell isformed, a porous support body is built off the back side of the shell toprovide the tool with the desired heat-exchanging characteristics.

[0011] The primary/fundamental concept of mold design and constructionis fulfilled, namely design and construct one piece molds having anopen, internal structure beneath the molding surface thus providing for:

[0012] a uniform and short path for thermal energy flowing from themolded part to the heat transfer fluid; a 10-15 fold increase overnon-porous molds in the surface area of the fluid side contact with theheat transfer fluid; turbulent flow of the heat transfer fluid at allnormal flow rates; and structures which will handle up to 10,000 psi incompression for aluminum and greater than 10,000 psi for otherconstruction materials such as steel or titanium.

[0013] The development of the porous support body begins with aplurality of discrete metallic elements that are capable of being bondedmetallurgically to one another and to the shell. The elements are packedtogether against the backside surface of the shell and are shaped suchthat when packed, the elements provide a network of interconnected openspaces extending throughout the packed mass of elements. The elementsand shell are united as a one-piece metallic structure by heating theelements and shell sufficiently to generate metallurgical bonds at thepoints of contact between contiguous elements and the shell, whileretaining the network of interconnected open spaces throughout the massof bonded elements.

[0014] The invention has several advantages over conventional formingtools of the solid block type described above and the earlyheat-exchanging tools disclosed in the aforementioned publishedapplication. One principle advantage is that the support body isas-formed to the shape of the preformed shell, eliminating the costlyand time consuming process of machining a contoured shaping surface froma solid or porous metal support body block.

[0015] The preforming of the metallic shell further dispenses with themulti-step process of thermal spraying metallic particles onto themachined contoured surface of the porous support body. In accordancewith the present invention, the metallic shell can be preformed by anyof a number of processes, including casting, stamping, powder metalforming, forging, and even thermal spraying if desired, thereby offeringa wide variety of options, some of which may be more suitable thanothers for any given manufacture. Stamping the shell, for example,provides a very quick, cost efficient way of producing the non-porousshaping surface of the forming tool, as opposed to machining the surfaceinto a solid block or developing the surface by thermal spraying moltenparticles of metal onto a contoured surface of a porous metal block.

[0016] The use of the metallurgically bondable metallic elements to formthe support body also has several advantages over the machine supportblocks (solid and porous) described above. One principle advantage isthat the elements are able to conform as a mass readily to the desiredshape of the support body and particularly to the backside surface ofthe preformed shell. This eliminates the need to machine a contouredsurface in the support body. Rather, the contour is as-formed with theformation of the support body.

[0017] Another advantage that the metallic elements provide is that whenpacked together, the mass is substantially porous. Throughout the massthere exists a network of interconnected open spaces or channels. Whenbonded together according to the invention, the porous network ispreserved, providing a more efficient, less costly approach to producinga porous support body than that of a machine porous block as disclosedin the aforementioned published application.

[0018] A still further advantage of the invention is that themetallurgical bonding of the packed elements to the shell unites thesupport body and shell as one integrated metallurgical structure. Assuch, a direct, continuous metallurgical and mechanical transition isprovided between the non-porous shell and the porous metal support body,uninterrupted by any gaps or interfaces at the transition, for quicklyand efficiently conducting heat from the shell to the porous supportbody.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Presently preferred embodiments of the invention are disclosed inthe following description and in the accompanying drawings, wherein:

[0020]FIG. 1 is a schematic, exploded cross-sectional view of theapparatus and component materials used for constructing a forming toolin accordance with a first presently preferred embodiment of theinvention;

[0021]FIG. 2 is an assembly view of the apparatus and components of FIG.1;

[0022]FIG. 3 is a schematic cross-sectional view of the forming toolproduced by the apparatus and material components of FIGS. 1 and 2;

[0023]FIG. 4 is an enlarged schematic cross-sectional view of theencircled area 4 of FIG. 3;

[0024]FIG. 5 is a still further schematic enlargement illustrating ingreater detail the metallurgical bond generated between contiguousmetallic elements and the shell of the tool;

[0025]FIG. 6 is a schematic cross-sectional view like FIG. 2 but of analternative embodiment of the invention; and

[0026]FIG. 7 is a cross-sectional view of the forming tool produced bythe apparatus and material components of FIG. 6.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0027] The invention is broadly related to forming tools of the typeused to impart a desired shape to articles of manufacture made from suchshapable materials as metal, plastics, resins, glass, composites, etc.Included among the forming tools contemplated are metal molds and diesused in the casting and forming of various metals and their alloys andcomposites; metal dies used in the injection molding and thermal formingof plastics, resins, glass; and various other shaping tools of thegeneral type disclosed in the aforementioned International PublishedApplication No. WO-96/17716, the disclosure of which is incorporatedherein by reference.

[0028] The invention is concerned more specifically with heat-exchangingforming tools employing a manufacturing process in which a porousmetallic support body is formed to shape against and metallurgicallybonded to a preformed non-porous metallic shell having an outercontoured surface corresponding in configuration to the shape to beimparted to an article of manufacture shaped by the tool. What resultsfrom the process is a one-piece metallic structure having a non-porouspreformed shell backed by an integrated support body comprised of aplurality of individual metallic elements bonded metallurgically to oneanother and to the shell in a manner to provide an interconnectednetwork of open pores or channels throughout the body defining atortuous flow path for the passage of a heat-transferring fluid throughthe body.

[0029] Such a heat-exchanging forming tool constructed in accordancewith a first presently preferred embodiment of the invention isillustrated schematically in FIG. 3 and designated generally by thereference numeral 10. The tool 10 includes a non-porous preformedmetallic shell 12 having an outer contoured shaping surface 14 having aconfiguration corresponding to that of a predetermined shape to beimparted by the tool to an article of manufacture (not shown). Forexample, the shaping surface 14 could represent one-half the cavity of amold or die for shaping molten metal, plastics, glass, etc.

[0030] Various techniques can be employed for producing the preformedshell 12. These include, but are not limited to, casting the shell toshape from molten metal, forming a sheet or plate of metal to shape toprovide the desired contour, machining the shell from a block of metalwhich is contemplated but less preferred due to the cost and timeinvolved, thermal spraying molten metal particles to the desired shapeof the shell, or forming the shell to shape using known powder metalforming techniques. The shell 12 is formed to have a generally uniformthickness such that a backside surface 20 of the shell 12 is contouredinversely to that of the shaping surface 14. The material for themetallic shell 12 may be any of numerous metals or their alloys orcomposites suitable for the application and the forming process employedto produce the shell 12. Suitable materials are given below.

[0031] The shell 12 is backed by a porous heat exchanging metallicsupport body 16. As shown, the body 16 may include a five-sided metallicenclosure or casing 18 joined to the backside surface 20 of the shell 12adjacent the perimeter of the shell enclosing space or chamber 22therebetween. A packed mass 24 of metallic elements 26 are housed withinthe chamber 22 and joined by metallurgical bonds across points ofcontact between contiguous elements 26 and at least the backside surface20 of the shell, and preferably to the walls of the enclosure 18 aswell. As such, there is a continuous metallurgical and mechanicaltransition from one portion of the forming tool to the next, andparticularly between the shell 12 and the porous metallic mass 24,providing a direct, uninterrupted flow path for the conduction of heatbetween the shaping surface 14 of the tool 10 and the porous supportbody 16, uninterrupted by gaps or transitional interfaces that woulddeter heat flow.

[0032] In addition to there being a direct metallurgical bond betweenthe shell 12 and support body 16, there is also provided aninterconnected network of open pores or channels 28 throughout thepacked metallic mass 24 and in communication with the shell 12. In thepreferred arrangement, the pores are distributed generally uniformlythroughout the support body 16 and particularly in the vicinity of theshell 12 to provide corresponding generally uniform cooling or heatingacross the shell. The open porous network 28 exposes a large surfacearea of the support body metal to the open network 28. In this way, theporous metal support body 16 acts likes a radiator and is able todisburse heat at a far greater rate than would a solid metal blocklacking such pores. The rate of heat transfer is enhanced still furtherby the introduction of a heat-exchanging fluid such as water or otherwell known flowable heating or cooling agents through the porous network28. The porous network 28 defines a tortuous flow path for the fluidthrough the body 16, imparting turbulent flow to the fluid as it movesthrough the body 16 even at low flow rates. Such turbulent flow at lowflow rates optimizes the cooling efficiency of the heat-transfer fluidand minimizes the expenditure of energy to attain turbulent flow.

[0033] It will be seen in FIG. 3 that openings 30 are provided in thewalls of the enclosure 18 which may serve as inlets and outlets for theheat transfer fluid passed through the support body 16.

[0034]FIGS. 1 and 2 illustrate how the tool 10 of FIG. 3 is producedaccording to the invention. As shown, a metal container 32 is providedhaving upstanding side walls 34. At the bottom of the container 32 is asupport block 38 having an upper support surface 40. The block 38 isfabricated preferably of an insulating material such as sand or ceramicgranules or the like shaped such that the upper support surface 40presents a contour that duplicates the shape of the article to be formedby the tool 10.

[0035] The shaping surface 14 of the shell is disposed face down on theupper surface 40 of the support block 38. As will be seen in FIG. 2, theshape of the upper surface 40 fully complements that of the shapingsurface 14 of, the shell 12 such that there is full surface-to-surfacecontact between the shell 12 and block 38.

[0036] A plurality of the individual, discrete metallic elements 26 arethen poured into the container 32 where they are packed together (eitherunder their own weight or by applied pressure) against the backsidesurface 20 of the shell 12 such that the mass of elements are conformedclosely to the shape of the backside surface 20. The elements 26 arefabricated of metallic material selected for the ability to bond theelements 26 metallurgically to one another and to the metallic shell 12and, if provided, to the metallic enclosure 18. It will be appreciatedby those skilled in the art that there are numerous metallics capable ofbonding metallurgically to one another, including pure metals, theiralloys and composites and combinations thereof. The selection of theparticular material or materials for the shell 12 and elements 26 willdepend in part on the particular end use of the forming tool and mayinclude considerations such as the required strength of the tool, thethermal conductivity requirements of the material, as well as materialavailability and cost considerations. Also a factor may be the processselected for generating the metallurgical bonds which may includebrazing, sintering, soldering, casting etc. The metallic materialscontemplated for the shell 12 and elements 26 may include, for example,aluminum, magnesium, copper, stainless steel, tool steel, nickel,nickel-aluminide, titanium, etc., to name a few.

[0037] Another characteristic of the individual elements 26 is that theyhave predetermined shapes that, when assembled in the packed mass 24,provide the network of interconnected open spaces or pores 28 throughoutthe mass. Various shapes may be employed depending upon the availabilityof the material and desired degree of porosity to be provided to thesupport body 16. Some of the shapes contemplated include, for exampleballs, beads, rods, jacks, wires, etc., or combinations thereof.

[0038] As shown in FIG. 2, the five-sided metallic enclosure 18 mayinitially comprise a separate component that is fitted down into thecontainer 32 after the elements 26 has been introduced such that thewalls of the enclosure 18 enclose the elements 26. Free ends or edges42, preferably confront the backside surface 20 of the shell 12 and thewalls of the enclosure 18 are preferably dimensioned to pack theelements 26 tightly against the shell 12 such that the elements 26 arein intimate contact with each other and with the shell 12 and enclosure18.

[0039] Once assembled, the elements 26, shell 12 and enclosure 18 areheated sufficiently to cause the elements 26 to bond metallurgicallyacross contiguous contact points with each other and with the shell 12and enclosure 18, while preserving the porous network 28 as illustratedschematically in FIGS. 3 and 4. As shown, the metallurgical bonding hasthe effect of uniting the elements 26, shell 12, and enclosure 18 as onecontinuous metallic structure.

[0040] As mentioned, sintering may be employed as the means of producingthe metallurgical bonds. In such case, it may be advantageous to coatthe elements 26 as well as the shell 12 and enclosure 18 with a suitablesintering flux which will act to cleanse the bonding surfaces ofimpurities, oxides, etc., that may otherwise inhibit the formation ofthe metallurgical bonds. The flux selected if and as required will beappropriate to the metallic materials involved as those skilled in theart will appreciate. Also, it will be appreciated that the appropriatesintering temperature may vary according to the materials involved butin any case will be heated to such a temperature and for a timesufficient to generate the metallurgical bonds.

[0041] Where soldering or brazing is employed as the means of producingthe metallurgical bonds, the contact surfaces of the elements 26, shell12 and enclosure 18 may be coated with a low melting point metallicmaterial 44 (FIG. 5) having a known fusing temperature that, when heatedto such temperature, will meld across contiguous points of contact togenerate the bonds. It is preferred that the brazing or soldering becarried out in an evacuated atmosphere. For this purpose, the chamber 22between the enclosure 18 and shell 12 can be sealed and evacuated toprovide such environment.

[0042] Various brazing and soldering materials may be employeddepending, to a large degree, on the metallic materials to be bonded andparticular end use requirements of the forming tool to be made,including the required strength and operating temperatures of theforming tool 10. During metallurgical bonding, the metallic coating 44may combine or alloy with the parent metal of the element 26, producinglocalized alloyed zones 46 at points of contact between contiguouselements and the interior surfaces of the shell 12 and enclosure 18 (SeeFIG. 5). Examples of suitable material combinations that would bond insuch manner include parent material of aluminum or alloys thereof forthe elements 26, shell 12, and enclosure 18, and zinc or alloys thereoffor the metallic coating 44. In such case, the assembly of the elements26, shell 12 and enclosure 18 would be heated to a temperature above themelting point of the zinc coating 44, whereupon the zinc would melt andalloy with the aluminum parent material at the points of contact togenerate the metallurgical bonds, as illustrated best in FIG. 5. Ofcourse, numerous other parent/coating combinations could be employed, aswill be appreciated by those skilled in the art.

[0043] A forming tool made in accordance with a second embodiment of theinvention is illustrated in FIG. 6 and designated generally by thereference numeral 110. The forming tool 110 is alike in all respectswith the forming tool 10 of the first embodiment except that theenclosure 18 has been omitted. The remaining features are the same andare referred to by the same reference numerals offset by 100.

[0044]FIG. 7 schematically illustrates the process for making theforming tool 110 employing a container 132 similar to that of thecontainer 32 except that the interior of the container 134 has anon-adhering coating or lining 48 applied thereto, such as a ceramiccoating or board, to which the metallic elements 126 will not bond. Inthis way, the porous support body 116 is releasible from the container132 following the formation of the tool 110. An enclosure similar tothat of enclosure 18 can be attached, if desired, in a subsequentjoining operation.

[0045] The disclosed embodiments are representative of presentlypreferred forms of the invention, and are intended to be illustrativerather than definitive thereof. The invention is defined in the claims.

I claim:
 1. A method of making a heat-exchanging forming tool for use inshaping articles of manufacture, comprising: providing a prefabricatednon-porous metallic shell having an outer contoured shaping surfacecorresponding to the shape to be imparted to the article to be formed bythe tool and an opposite backside surface; providing a plurality ofdiscrete metallic elements metallurgically bondable to each other and tothe backside surface of the shell; assembling the metallic elementsagainst the backside surface of the shell and in contact with oneanother to provide a packed mass of such elements, the elements beingshaped such that when packed together the elements provide a network ofinterconnected open spaces throughout the packed mass of the elements;and metallurgically bonding the packed metallic elements to one anotherand to the shell while preserving the network of interconnected openspaces between the elements thereby obtaining a one-piece structurecomprised of the non-porous metallic shell backed by an integratedporous metallic support body through which a heat exchanging fluid maybe passed to conduct heat to or from the shaping surface of the shell.2. The method of claim 1 wherein the metallic elements are packed andbonded within a container extending from the backside surface of theshell such that the structural support body assumes the shape of theinterior of the container and the backside surface of the shell.
 3. Themethod of claim 2 wherein the support body is releasable from thecontainer.
 4. The method of claim 2 wherein the container includes aninsulating base having an upper support surface contoured inversely tothat of the shaping surface and side walls extending upwardly of thesupport surface.
 5. The method of claim 4 wherein the shaping surface ofthe shell is supported face down on the support surface of the base andthe side walls of the container are extended upwardly from the backsidesurface of the shell.
 6. The method of claim 5 wherein the side wallsare lined with insulating material to prevent bonding of the supportbody to the side walls.
 7. The method of claim 4 wherein the metallicelements metallurgically bond to the walls of the container such thatthe walls of the container become an integrated portion of the formingtool.
 8. The method of claim 7 wherein the mass of metallic elements areencased by the container.
 9. The method of claim 1 wherein themetallurgical bonding results from sintering the metallic elements andshell at an elevated sintering temperature.
 10. The method of claim 1wherein the metallic elements are coated with a low melting pointmetallurgical bonding metal and are heated to a temperature sufficientto fuse the coatings of contiguous metallic elements to one another andto the shell thereby producing the metallurgical bonding of the elementsand shell.
 11. The method of claim 10 wherein the bonding metal alloyswith the metal of the metallic elements and shell.
 12. The method ofclaim 1 wherein the metallic shell comprises a preformed cast member.13. The method of claim 1 wherein the metallic shell comprises apreformed metal plate member.
 14. The method of claim 1 wherein themetallic shell comprises a preformed thermal-spayed member.
 15. Themethod of claim 1 wherein the preformed shell is a machined member. 16.The method of claim 1 wherein the preformed shell is fabricated frompowder metal.
 17. The method of claim 1 wherein the preformed shell isformed with a generally uniform thickness.
 18. The method of claim 1including supporting the shell shaping surface down on an insulatingsupport member and arranging a five-sided metallic enclosure about themass of metallic elements with an open end of the enclosure confrontingthe backside surface of the shell thereby providing a chamber housingthe metallic elements, and heating the shell, elements and enclosuresufficiently to bond the elements to one another and to the shell andenclosure.
 19. A method of making a heat-exchanging forming tool for usein shaping articles of manufacture, said method comprising the steps of:forming a non-porous metallic shell of generally uniform thicknesshaving an outer contoured shaping surface of predetermined configurationcorresponding to the desired shape to be imparted to the article by thetool on the opposite backside surface inversely contoured to that of theshaping surface; supporting the shaping surface of the shell face downon an insulating support member such that the backside surface of theshell faces upwardly; arranging a container over the shell; introducinga plurality of discrete metallic elements into the container to providea packed mass of such elements in contact with each other and with thebackside surface of the shell and surrounding walls of the container,the elements being shaped such that when packed together the elementsprovide a network of interconnected open spaces throughout the packedmass of the elements; and heating the elements and shell sufficiently tometallurgically bond the packed metallic elements to one another and tothe shell while preserving the network of interconnected open spacesbetween the elements thereby obtaining a one-piece structure comprisedof the non-porous metallic shell backed by an integrated porous metallicsupport body through which a heat exchanging fluid may be passed toconduct heat to or from the shaping surface of the shell.
 20. Aheat-exchanging forming tool for use in shaping articles of manufacturecomprising: a non-porous preformed metallic shell having an outershaping surface of predetermined contour corresponding in configurationto the desired shape to be imparted to the article by the tool; and aporous heat-exchanging support body having a plurality of individualmetallic elements packed together and against a backside surface of saidshell and bonded metallurgically to one another and to said shell acrosscontiguous points of contact while providing a network of interconnectedopen spaces throughout the support body defining a tortuous flow paththrough the support body through which a heat exchanging fluid may bepassed to conduct heat to or from the shaping surface of the shell.